Principal Commercial Commitments under Repurchase Agreements and Dealer Inventory Financing Guarantees (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Oct. 31, 2012
Guarantee On Dealer Inventory Financing
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Total Amount Committed	$ 900
Term of Commitments	Various
Standby Repurchase Obligations On Dealer Inventory Financing
Purchase Commitment, Excluding Long-term Commitment [Line Items]
Standby Repurchase Obligations Amount	$ 963,211
Term of Commitments	Up to eighteen months